A FREE Auto/Truck 14V Electrical
Systems Testing Tutorial

Electrical Systems Testing Flip-Chart
Shows you how!

This free tutorial is provided on testing a vehicle's primary 14V electrical system. A vehicle's primary electrical system consists of the battery, the generator (formerly called an alternator) and the engine and accesssory grounds. With FIRST THINGS FIRST™ you can test the battery, engine and accessory grounds and perform a thorough charging voltage analysis in 5-8 minutes with a little practice using our FIRST THINGS FIRST™ flip-chart.

begins with electrical tests before the engine is cranked, when the vehicle is first started and electrical testing continues through engine warm-up to ensure that there are no primary electrical system problems in the primary electrical system that will affect vehicle performance and driveability.

The complete step-by-step electrical system test procedure using only your DMM is contained in our electrical troubleshooting flip-chart we call FIRST THINGS FIRST™because it's the FIRST thing to do - electrically.

 A laminated flip-chart version is available for the professional technician to purchase for $79.00 plus S/H.
Read the following tutorial of
FIRST THINGS FIRST™ to get an idea of the effectiveness of using FIRST THINGS FIRST™ without the need for extensive electrical training to use the flip-chart. Please feel free to print out your own copy of this tutorial.

Overview Of A Vehicle's Primary Electrical System
The generic block diagram of a car or truck's primary 14V electrical system is shown in Figure 1 and is the schematic diagram used in the flip-chart FIRST THINGS FIRST™. The illustration consists of a Battery, and an Generator (Alternator) which is referred to by the name "generator" (an old term coming back into use since 1996) and the vehicle's Primary Ground System consisting of an Accessory Ground and an Engine Ground. To become more familiar with a vehicle's primary electrical system, trace the wires in Figure 1 between all components to see how they connect together.

The Battery
 The vehicle's battery stores electrical energy in chemical form and delivers large amounts of electrical energy (current) on demand to crank the engine. Identify both battery posts on the battery in Figure 1. One post is marked "+" (positive) or "hot" side and has a red or black battery cable connected to it. The Junction Block is a voltage side common connection point used on many vehicles. It is located in the engine compartment near the battery. The negative battery post is marked "-" (minus) and is called "ground.". The negative battery cable is usually a two wire black cable. The smaller diameter cable is connected to the sheet metal for the Accessory Ground. The larger diameter wire is connected to the engine block for the Engine Ground.

The Generator (Alternator)
 The generator (alternator) produces a charging voltage to electrically power the vehicle and recharge the battery as long as the engine is running and the alternator is performing properly. The positive output terminal of the alternator, called the "B+" terminal, is a large insulated terminal on the rear or side of the generator (alternator) housing with a heavy gauge wire connecting back to the battery's positive (+) post through the Junction Block. The generator (alternator) housing is the generator (alternator)'s negative (-) terminal (or ground).

Trace both the positive and negative battery cables from the battery posts to their connection points in the vehicle. Battery "+" goes to generator (alternator) "+" (the B+ terminal) through the wiring harness. Battery "-" goes to generator (alternator) "-" through the engine ground and the engine block. The purpose of the voltage regulator is to excite the generator (alternator) and prevent the charging voltage from rising above a preset limit. The voltage regulator may be mounted external to the alternator and bolted to the vehicle's sheet metal with wires connecting to the generator (alternator) or it may be mounted inside the generator (alternator). On many newer vehicles the voltage regulator may be computer controlled by a vehicle computer for more precise control of the charging voltage. This flip-chart may be used regardless of where the voltage regulator is mounted. Testing the primary electrical system using
FIRST THINGS FIRST™ requires only a digital voltmeter (DMM).

Do This On A Vehicle First
Look under the hood of the car or truck to be tested and make sure all connections and wires around the battery and generator (alternator) are tight, in good condition with no corrosion or damaged insulation. Identify both "+" and "-" battery posts and visually inspect for corrosion around the battery cable terminals where corrosion is normally a big problem. Tug on the battery cables to make sure that corrosion has not caused the cable ends to form a bad connection where the cable enters the battery cable terminal end. Next, locate the generator (alternator) and the B+ terminal. Inspect the wire at the generator (alternator)'s B+ terminal to make sure it is clean and making a tight connection.

What You Need To Know About Digital Multimeters (DMMs)
 There are two types of DMMs in use. (1) Autoranging DMM automatically selects the proper range for a DC Voltage being measured. (2) Manually Selected DMM requires the technician to manually select the correct voltage range using the main function knob.

Autoranging DMM

 A block diagram of an Autoranging DMM is shown in (1) of Figure 2. Note the symbol for the DC Voltage function. It is a small solid line above a small dotted line followed by a "V". This means "DC Volts." By selecting DC Volts, an Autoranging DMM automatically sets to the lowest milli-volt (mV) DC Voltage range, usually 200, 300, or 400 mV depending on the DMM brand. All DMMs display 00.0 or 000.0 when on the milli-volt range so 100 mV (or 0.10V) would read as 100.0 (mV). When an Autoranging DMM senses the test voltage is above the value of the milli-volt range, the DMM automatically steps up to the next higher voltage range which is 2.00, 3.00 or 4.00 V DC range, depending on the DMM brand. All DMMs display .000 on the 2/3/4 volt range so 1.5 volts would read as 1.500 (V).

When an Autoranging DMM senses the test voltage is above the value of the 2/3/4 Volt range, the DMM automatically steps up to the next higher voltage range which is the 20.00, 30.00 or 40.00 V DC range, depending on the DMM brand. This is the highest range the DMM must "step-up" to since cars and trucks run on 12-15 volt systems and no voltage greater than 20 volts is measured. All DMMs display 0.00 on the 20/30/40 Volt range so 14.25 volts would read as 14.25 (V).

If 145 mV is measured, the DMM drops back down to the mV range and reads 145.0 mV. As an Autoranging DMM jumps around between the mV, 2/3/4V and 20/30/40V ranges, it can get very confusing and cause reading errors which lead to misdiagnosis when troubleshooting. If using an Autoranging DMM here's how to make it easy and avoid the confusion caused by the DMM automatically changing voltage ranges between test steps.

Manually select the 20V, 30V or 40V range which ever your DMM has and leave it there while performing these FIRST THINGS FIRST electrical tests. Simply press the RANGE BUTTON until the readout first says 0.00. This is the 20, 30 or 40 Volt range and a ten millivolt reading is 0.01 while a 14 volt reading is 14.00. The 20V, 30V or 40V range is the best DMM range for performing the electrical tests as explained in FIRST THINGS FIRST.

Manually Selectable DMM
  A manually selected DMM, is represented in (2) of Figure 2 and is easier to use. They have a main function knob in the center of the DMM face plate that permits a technician to manually select the desired range. Manually select the 20/30/40 Volt ranges. The readout should read 0.00. The DMM then stays on the 20/30/40 volt range for all tests. Leave the knob set to 20/30/40 volt range for all the test steps. A comparison of voltage readings for both types of DMM is shown in Figure 2.

Use Either Type DMM (Autoranging or Manually Selected)
Select the 20, 30, or 40 DC voltage range on the DMM. This is when the DMM first indicates 0.00. Leave the DMM on this range for all tests. DO NOT ALLOW THE DMM TO AUTO-RANGE DURING MEASUREMENTS AS IT COULD CAUSE CONFUSION INTERPRETING READINGS WHICH WILL VARY BETWEEN VOLTS AND mV. Place the DMM test leads into the vehicle as shown in the illustration for each test step and follow the written instructions on the left side of the page for that step. Compare your DMM reading with the diagram of each test. The text discusses what to do if an incorrect reading is obtained. Follow directions given on each page for repair procedures. Step 1 is provided so you can sample the format.

How To Use The Test Procedure - FIRST THINGS FIRST™

Each of the 15 test steps are explained and illustrated on their own page. On the left side of the page are instructions on how to perform each test step. On the right side of the page is a picture of the primary electrical system showing how the DMM test leads placed into the vehicle to make each measurement. Follow the illustration of the DMM test leads when connecting your DMM to the vehicle. The DMM also shows the approximate reading you should find in the vehicle. Compare your DMM reading with the reading in the illustration. If the reading can be a little higher or a little lower than what is shown in the illustration, the text will explain the acceptable upper and lower limits of a reading needed to pass or fail a test step and what should be done to correct a problem.

Connect your DMM Test Leads to the DMM as shown in the illustration to the right. The Red (+) DMM Test Lead connects to the V/Ohm jack. The Black (-) DMM Test Lead connects to the COM (Common) jack. Here is a sample of how FIRST THINGS FIRST™ guides you through each step with these paragraph titles.:
Title of the measurement
Do This . . . .
Expect This . . . .
Tips . . . .

Here's a sample of FIRST THINGS FIRST™ Step 1 . . . . . . .

Step 1: Measure Battery Open Circuit Voltage

Do This:
This paragraph explains the exact procedure to follow to perform the test step. For example, it will say "with the ignition key OFF, measure the battery terminal post voltage." The illustration also shows how the test leads are connected into the vehicle. Follow the illustration.

Expect This:
This paragraph explains the expected result so it can be determined that the vehicle passes or fails a test. Also included are the range of readings that should be expected in this test. If the reading is a little lower or a little higher, the exact numbers are given in the text for comparison with what is found in the vehicle to determine pass or fail.

 The paragraph "Expect This:" suggests items to check if the reading is incorrect (too high or too low) and the vehicle fails a test step. Also listed are items to double check to avoid common mistakes made when performing each test step. When the vehicle passes each test step, go to the next page and perform the next step. Do not move to the next step until the correct reading is obtained from either the vehicle passing the test or as a result of a suggested repair procedure correcting a problem.

Tips: Some of the test steps offer tips on what to check next if a DMM reading on a particular test step is too high or too low.

 The remaining electrical system test Steps 2-14 are found in FIRST THINGS FIRST.™ Order below!

When you first receive your copy of
FIRST THINGS FIRST™READ THROUGH All 14 STEPS FIRST to get familiar with the tests.
Then begin performing FIRST THINGS FIRST™. Go slow the first time you perform the electrical tests to thoroughly read through and understand what you are doing. Then practice all 15 test steps and record readings on the page "Test Results Record" provided on the last page of each flip-chart.

Feel free to make extra copies of the Test Results page to record test results. Show or give the copy to your customer with the readings found during the tests.

With a little practice most technicians can perform the electrical tests in FIRST THINGS FIRST in 5 minutes.

This tutorial reviewed basic concepts of a vehicle's primary electrical system and appropriate electrical system test procedures with an introduction to FIRST THINGS FIRST.™
To order a laminated copy of

simply click on the red "ADD-TO-CART button, $79.00 plus s/h. We'll include information about our other training programs you can study at home.

Would you like more training in vehicle electrical-electronics troubleshooting? We have the training for you, either home study or live training presented on-site by Vince Fischelli.

To those techs who like training material in printed form look at our 60 lesson home-study course in vehicle electrical - electronics troubleshooting click here. Now also available on-line with lifetime access and you can print out your own lessons.

To those techs who prefer more of a hands-on approach to electrical training look at our hands-on home-study vehicle electrical - electronics troubleshooting training program
click here.

If you would like to attend live electrical - electronics troubleshooting training workshops in Dallas personally taught by Vince Fischelli click here for information.

If you're a SHOP OWNER click here This web page is just for shop owners.

If you're a Tech School Teacher
click here This web page is just for teachers.

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Veejer Enterprises Inc.
Garland, Texas 75042-5419
Phone:  972-276-9642
Fax:     972-276-8122
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